Tetra-arm polyethylene glycol(Tetra-PEG) gels are formed by cross-linking of two types of tetra-armed star polymers, and are expected to be applied as a biomaterials because of its high mechanical strength and biocompatibility. In order to insert the gel into the body, it is necessary to prepare the gel in a dilute system to prevent swelling, but there is a problem that it takes a long time for the gelation in a dilute system. In this study, we focused on the molecular crowding effect that accelerates the reaction in dilute systems, and analyzed the effect on gelation by reproducing the molecular crowding environment by introducing a large amount of guest polymer that does not react with Tetra-PEG prepolymer into the system. As a result, it was confirmed that the addition of the guest polymer changed the gelation process in the dilute system and shortened the gelation time.